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How is anal cancer staged?

The stage of a cancer is a standard way for doctors to sum up how far a cancer has spread. The stage is important because treatment options and outlook for recovery and survival depend on the cancer’s stage. If you have anal cancer, ask your cancer care team to explain its stage in a way that you understand. This can help you take a more active role in decisions about your treatment.

The most common system used to stage anal cancer is the TNM system of the American Joint Committee on Cancer (AJCC). This system is used only for tumors in the anal canal, not those that are only in the anal margin or perianal skin.

The TNM system

The TNM system for staging contains 3 key pieces of information:

T describes the size of the primary tumor, measured in centimeters (cm), and whether the cancer has spread to organs next to the tumor.

N describes the extent of spread to nearby (regional) lymph nodes (bean-sized collections of immune cells to which cancers often spread).

M indicates whether the cancer has metastasized (spread) to other organs. (The most common sites of spread are the liver and lungs.)

Numbers or letters appear after T, N, and M to provide more details about each of these factors:

The numbers 0 through 4 indicate increasing severity.

The letter X means “cannot be assessed” because the information is not available.

T categories for anal cancer

TX: Primary tumor cannot be assessed

T0: No evidence of primary tumor

Tis: The cancer is only in the mucosa (the top layer of cells lining the inside of the anus). It has not started growing into the deeper layers. This is also known as carcinoma in situ (CIS).

T1: The tumor is 2 cm (about 4/5 inch) across or smaller

T2: Tumor is more than 2 cm but not more than 5 cm (about 2 inches) across

T3: Tumor is larger than 5 cm across

T4: Tumor of any size that is growing into nearby organ(s), such as the vagina, urethra (the tube that carries urine out of the bladder), prostate gland, or bladder

N categories for anal cancer

NX: Regional (nearby) lymph nodes cannot be assessed

N0: No spread to nearby lymph nodes

N1: Spread to lymph nodes near the rectum

N2: Spread to lymph nodes on one side of the groin and/or pelvis

N3: Spread to lymph nodes near the rectum and in the groin or pelvis, or to both sides of the groin or pelvis

M categories for anal cancer

M0: No distant spread

M1: Distant spread to internal organs or lymph nodes of the abdomen

Stage grouping

Once the T, N, and M categories have been assigned, this information is combined to assign an overall stage of 0, I, II, III, or IV. The stages identify cancers that have a similar prognosis (outlook) and thus are treated in a similar way. Patients with lower stage numbers tend to have a better outlook.

Stage 0: Tis, N0, M0

Stage 0 is very early cancer (or pre-cancer) that exists only in the top layer of anal tissue. This stage is also known as carcinoma in situ (CIS) or Bowen disease.

Stage I: T1, N0, M0

The cancer cells have spread beyond the top layer of anal tissue. The tumor is less than 2 cm (about 4/5 inch) across (T1). It has not spread to nearby lymph nodes (N0) or distant sites (M0).

Stage II: T2 or T3, N0, M0

The cancer is larger than 2 cm across, but it has not grown into nearby organs (T2 or T3). It has not spread to nearby lymph nodes (N0) or to distant sites (M0).

Stage IIIA: Either of the following:

T1-T3, N1, M0: The cancer can be any size, but it has not grown into nearby organs (T1-T3). It has spread to the lymph nodes around the rectum (N1). It has not spread to distant sites (M0).

T4, N0, M0: The cancer has grown into nearby organs, such as the vagina or the bladder (T4). It has not spread to nearby lymph nodes (N0) or to distant sites (M0).

Stage IIIB: Either of the following:

T4, N1, M0: The cancer has grown into nearby organs, such as the vagina or the bladder (T4), and has also spread to lymph nodes around the rectum (N1). It has not spread to distant sites (M0).

Any T, N2 or N3, M0: The cancer can be of any size and may or may not have grown into nearby organs (any T). It has spread to lymph nodes in the groin or pelvis, with or without spread to lymph nodes around the rectum (N2 or N3). It has not spread to distant sites (M0).

Stage IV: Any T, Any N, M1

The cancer can be any size and may or may not have grown into nearby organs (any T). It may or may not have spread to nearby lymph nodes (any N). It has spread to distant organs or tissues (M1).